A variety of polymeric materials are used in insulating, semiconducting and jacketing layer of electrical devices. In particular, low density polyethylene (LDPE) produced by high pressure free radical polymerization, and linear low density polyethylene (LLDPE) produced by Ziegler-Natta-catalyzed polymerization, are widely used. These materials are typically crosslinked to improve various properties such as mechanical strength, processability, and resistance to high temperature degradation.
Crosslinked LDPE offers a number of advantages over crosslinked LLDPE. In particular, LDPE has better processability characteristics, such as lower melt fracture, higher melt strength, and reduced torque requirements in extrusion. The electrical properties of LDPE insulators are also superior to those of LLDPE-based insulators, since the LDPE resin includes no residual, conductive catalyst. Despite the processability disadvantages of Ziegler-Natta LLDPE, LLDPE is widely used in electrical applications, due to significant advantages in mechanical strength both before and after aging, in crosslinking speed, and in overall improved cost/performance balance.
There remains a need in the art for crosslinkable and crosslinked polymer compositions which combine the processability advantages of LDPE and the mechanical strength and crosslinking speed of Ziegler-Natta LLDPE.